The present invention concerns an air purifier intended to be used, for instance, as a so-called grease filter in the air venting systems of institutional, bar, grill room and restaurant kitchens or equivalent spaces, said air purifier comprising a purifier part which has of two or more air purifying modules operating on the centrifugal separation principle, each of them having one or several vortex chambers, and air purifier frame structures, if any.
An important field of use of air purifiers is the so-called grease filters. Through the grease filters, spoiled air is drawn in connection with food preparation. In professional kitchens, such as restaurant, grill room and institutional kitchens, the air that is spoiled in connection with the preparing of food causes a special problem.
The grease filter separates grease and other impurities from the vapors and gases produced when food is being prepared and in this way prevents the entry of these inflammable and otherwise harmful substances in the ventilation system. The grease filter is most often placed in air venting means over the stove or equivalent. Several grease filters may be used side by side.
The object of the grease filters is to prevent the duct systems and fans from becoming dirty and thus to reduce the need for cleaning the ventilation system and to improve fire safety and hygiene. The following requirements, among others, are imposed on a grease filter; naturally, good filtering capacity. The degree of self-cleaning of the filters based on running down of the accumulated grease should be as good as possible. The filter cleaning period should be long without increasing the resistivity of the filter or altering its cleaning efficiency. The filter should be easy to service and to inspect. The filter should present the highest possible fire safety and hygienic standard.
The filter should also be durable and user-friendly.
At a present, so-called impact filters are commonly used for grease filters which consist of mutually superimposed metal nets or of nets and a metal fiber mat. A drawback of these kinds of filters is that their separating capacity is usually too low. The filter needs frequent servicing because the grease adheres to the filter material instead of running down into the grease groove. Cleaning is difficult. These drawbacks also have the consequence that fire hazard increases, and the specific pressure loss increases significantly in comparison with a clean filter, whereby the quantity of vented air decreases and the quality of the indoor air deteriorates. The service life of such filters is relatively short. They are easily damaged at mounting, in use, or when they are being cleaned.
For grease filters, so-called centrifugal filters are also used. Present-day centrifugal filters also have comparatively low separating capacity, owing to their construction. As examples of inappropriate shaping of the elements in grease filters, the U.S. Pat. Nos. 3,834,135; 3,910,782; and 3,566,585 may be mentioned. Their construction is also unnecessarily complex and the filter is relatively expensive for this reason. The separating capacity of centrifugal filters as well as impact filters varies greatly in practice, depending on the amount of air flow. Attempts have been made to eliminate this drawback by means of adjustable filters. When several adjustable filters are used with different settings in one kitchen, there is a risk that they become mixed up e.g. after washing.
GB-A-2,092,483 teaches a conventional air purifier with centrifugal separators, where the outlet pipes 22 (FIGS. 4, 6 and 7) are merely central tubes or conduits of a conventional cyclone separator. It is emphasized that the direction of flow of a gaseous fluid reverses by 180.degree. in the conduits 22. This is best seen in FIGS. 4, 6 and 7, as denoted by the arrow Q3. Accordingly, this known air purifier suffers from a strong tendency to become clogged. Additionally, the air purifier according to GB-A-2,092,483 has a comparatively complicated structure, wherein a flow channel 12 extends over the entire length of the air purifier supplying air flow into each particular vortex chamber 4, 6, 8, 10 (FIG. 1). The particulates separated from the air flow continue to flow toward the outlet 20. Furthermore, as explicitly illustrated in GB-A2,092,483, the start of the escape point, or the inner end of the central tube 22 of the cyclone separator, is centered therewithin.
Certain advantages are however achieved with centrifugal filters. The service life of centrifugal filters is in general rather long. The filter efficiency also does not deteriorate as a consequence of repeated washing as is the case with fiber filters. The fire safety of centrifugal filters is also better than that of fiber filters.
In the centrifugal filters known in the art, the air flow turns 180.degree. in the lower cyclone cone, after which the air flow exits from the cyclone through the central tube. For this reason the filtering capacity is rather low and does not increase significantly after the change of direction. It is true that the separating capacity can be somewhat improved with the aid of vortices. The centrifugal filter does not store grease in the filter because the separated grease runs off efficiently. However, other solid particles also usually accompany the grease, e.g. dirt, dust, etc., and in this case the respective impurity is no longer freely flowing and fails therefore to run off even a slippery surface. This is the reason why existing centrifugal filters may become clogged.
Currently, such grease filters are also in use in which two consecutive filters are used. These so-called two-phase filters are good in principle, but if in both filters both phases are filtering out the same particle size, then the latter phase is unnecessary in practice because the filtering capacity only increases about 1% in comparison with the filtering capacity of the first filter.